1. Field of the Invention
This invention generally relates to tuning an electrical circuit network, and more particularly, to a tuning circuit for the electrical circuit network.
2. Description of the Related Art
Circuit technology for use as a filter or other tuning mechanism for an electrical circuit is known. A basic filter for an electrical circuit is a well-known resistive-capacitive (“RC”) circuit, inductive-capacitive (“LC”) circuit or resistive-inductive-capacitive (“RLC”) circuit.
Electrical filters and matching networks are frequently constructed as a “ladder” network. The ladder network consists of a number of shunt circuit elements that are electrically interconnected using series coupling elements. The shunt elements may be collections of reactive lumped elements such as resistors, capacitors, and/or inductors, or they may be distributed components such as small sections of transmission lines. The coupling elements may similarly be comprised of reactive lumped elements or transmission-line sections. The shunt elements and coupling elements may also be resonant or non-resonant, depending on the specific filter implementation and the desired electrical characteristics. For example, many bandpass filter designs use shunted short-circuited transmission-line resonators that are capacitively coupled together.
A problem with a conventional ladder network is that it is often sensitive to slight variations in any of its components values. For example, small deviations in any element value as a result of mechanical tolerances in the manufacturing process can degrade the electrical characteristics of the entire network. Another problem with a conventional ladder network is that it is often inflexible. Specifically, tuning the network is cumbersome and time-consuming because any changes to any element may result in changing the values of other elements to achieve the desired electrical characteristics.
Conventional solutions for tuning circuits may include use of a voltage-variable capacitor (“varactor”) in the ladder network. A varactor adds flexibility for tuning a circuit because the capacitance can be tuned by changing a bias voltage across the capacitor. However, conventional varactors made from gallium arsenide (“GaAs”) have relatively higher radio frequency (“RF”) losses, poor power handling, poor intermodulation distortion (“IMD”), and are expensive to produce.
Therefore, there is a need for a tunable circuit that allows for adjusting circuit characteristics on an ad hoc basis and that allows for adjusting electrical characteristics so that a single network can be used for multiple functions. Moreover, from both manufacturing and operational standpoints, there is a need for a filter structure with adjustable component values that also has strong power handling capabilities and is relatively inexpensive to produce.